The present invention relates to an apparatus for data storage system for recording signals as magnetization in the direction of thickness of a magnetic recording medium, and magnetically reading the signals.
The conventional recording technology is described hereinafter by taking an example of a perpendicular magnetic hard-disk drive. The perpendicular magnetic hard-disk drive refers to a magnetic hard-disk drive comprising a perpendicular recording medium, a read-write head, and so forth, for executing read-write by means of a perpendicular magnetic recording system. The perpendicular magnetic recording system is a system in which recording magnetization is formed in the direction of thickness of a medium in contrast to the conventional longitudinal recording system.
In FIG. 13, a perpendicular recording medium 13 has a recording layer 131 having magnetic anisotropy in the direction of thickness thereof. There are a single-layer recording medium having the recording layer 131 only, and a multilayer recording medium having a soft under layer 132 between the recording layer 131 and a board 133 (the recording medium hereinafter refers to the multilayer recording medium unless explicitly described otherwise). The recording layer 131 is made up of a perpendicularly magnetized film having high coercivity in order to retain information, and the soft under layer 132 has a property of undergoing magnetization when a magnetic field is applied thereto while reverting to a non-magnetized state when the magnetic field is removed. For a read-write head 140, use is generally made of a read-write-separation type head, comprising a recording element and a reading element. The recording element includes a ring type head in a ring-like shape, provided with a gap in a part thereof, for executing recording with a leakage magnetic field from the gap, for use in the longitudinal recording system as well, and a single pole type (SPT) magnetic head comprising a main pole, and an auxiliary pole (a write head hereinafter referred to as the SPT magnetic head unless explicitly described otherwise). Further, for the reading element, use is made of a magneto-resistive (MR) head capable of detecting changes in a magnetic field as changes in resistance.
Now, taking an example of a case where the SPT magnetic head 140 is combined with the multilayer recording medium 13, recording operation is broadly described hereinafter. A main pole 141 is magnetized by a magnetic field generated by a current flowing through coils 143 wound around the upper part of the recording element. Because an area of the tip of the main pole, facing the medium, is small, magnetic fluxes 50 converge thereon, so that a very large magnetic field is generated directly underneath the main pole, thereby effecting recording. The magnetic field penetrating through the recording layer 131 magnetizes the soft under layer 132. Meanwhile, an auxiliary pole 142 is magnetized by the magnetic field generated by the coils, in a direction opposite from the direction of the main pole 141, however, because an area of the tip of the auxiliary pole 142 is large, a magnetic field generated is small, and no recording is implemented. However, since the magnetic field in the direction opposite from the direction of the main pole is produced in the soft under layer, directly underneath the auxiliary pole, a magnetic field joining a portion of the soft under layer, directly underneath the main pole, with the portion thereof, directly underneath the auxiliary pole is formed in the soft under layer. At this point in time, a recording magnetic field 50 constitutes a path leading from the main pole to the auxiliary pole via the soft under layer. The MR head is provided with a MR element 146 sandwiched between upper and lower read shields 144, 145.
As shown in FIG. 14, in the case where a stray field 51 in a direction perpendicular to the surface of a medium is applied to such a recording system as described, the stray field 51 passes through the main pole, and the auxiliary pole. In such a case, because of the structure of the main pole 141, the stray field converges (511) on the tip of the main pole, so that there can occur a case where a magnetic field so strong as to cause decrease or demagnetization to occur to recording magnetization of the recording layer 131 is produced even when the stray field 51 applied from outside is weak. This is a phenomenon called decrease in recording magnetization or demagnetization of recording magnetization by the agency of a stray field. If this phenomenon occurs, not only recorded information is lost, but also even a servo-mark and identification signals for tracks and sectors are lost in the extreme case, thereby raising a possibility of causing interference with operation of a hard disk drive (HDD) itself.
There have been long recognized problems occurring when a stray field in a direction perpendicular to a recording medium is applied. With reference to the problems, a method of increasing resistance to a stray field by disposing a member having a magnetic shielding effect in a plane region of a HDD case opposite to a moving range of a magnetic head, and in side-face regions thereof connected to the plane region, has been disclosed in, for example, JP-A No. 77266/2003. Further, a technology whereby a member having a magnetic shielding effect is used not only in a moving range of a magnetic head but also on the whole surface of a HDD case has been disclosed in JP-A No. 95177/2004. In JP-A No. 197619/2002, there has been disclosed a technology for shielding a stray field by covering a main pole of a SPT magnetic head with a member having a magnetic shielding effect. In JP-A No. 47110/2004, there has been disclosed a method for shielding a stray field by covering a medium with a magnetic component in a shape resembling the letter U, disposed on a side of a spindle, opposite from a head. Further, other technologies have been disclosed in JP-A No. 210826/1993, JP-A No. 307002/1995, JP-A No. 84120/1994, and JP-A No. 45008/2003, respectively.